Summary On 30November 1996, the Maltese product carrier G.ORDZHONIKIDZE, carrying 15,348 metric tons of vegetable oil, was proceeding along the St.Lawrence river from Belawan, Indonesia, bound for Montreal, Quebec. Abreast of the Saint-Augustin Shoal on the St.Lawrence River, the G.ORDZHONIKIDZE grounded on the north edge of the channel when the bulk carrier LT ARGOSY was overtaking it. The G.ORDZHONIKIDZE sustained minor damage, and no pollution resulted. The vessel was refloated without assistance during the next rising tide. Ce rapport est galement disponible en franais. Other Factual Information Particulars of Vessels At about 0250[2] on 30November 1996, the G.ORDZHONIKIDZE arrived at the Quebec City pilotage station. Two pilots boarded to take turns conducting the vessel, which was proceeding toward Montreal at a surface speed of approximately 11.5 knots against the ebb tide. At about 0311, the LT ARGOSY also reached the Port of Quebec City. Following a change of pilots, the vessel continued on its way to Montreal at a speed of approximately 12.5knots. Visibility was good, with a light wind from the north-northeast, and a light snowfall. At 0430, one of the pilots of the G.ORDZHONIKIDZE reported to Marine Communication and Traffic Services (MCTS) in Quebec City that the vessel had cleared the Saint-Nicolas calling-in point. At about 0433, an agreement to let the LT ARGOSY overtake the G.ORDZHONIKIDZE was made between the pilots who had the conduct of the two vessels. Neither of the pilots informed the other that his vessel had a deep draught. The pilots intended to carry out the overtaking manoeuvre upstream of buoyQ22, but they did not confirm this verbally. Off Pointe Deschambault, the vessels were steered on the Saint-Augustin route using the Pointe--Basile range aft of the vessel. At 0437 the LT ARGOSY reached the Saint-Nicolas calling-in point. Although the Vessel Traffic Systems: Operations Manual (TP 1526) states that the traffic regulator must advise the pilots of ships of any pertinent information in his possession, the pilots were not informed by MCTS that the two vessels each had a deep draught. As agreed between the pilots, the G.ORDZHONIKIDZE was manoeuvred toward the north side of the channel between buoys Q18 and Q20 to let the LT ARGOSY pass on the south. Radar was not used to determine the safe limit of navigation along the north edge of the channel. At 0441, the speed was reduced to half ahead and then slow ahead. The overtaking manoeuvre was carried out by visual observation. The G. ORDZHONIKIDZE rounded buoy Q20 at a distance of approximately one ship length while the LTARGOSY overtook it. The pilot not on duty felt an abnormal vibration. The vessel immediately touched the north edge of the channel and then grounded between buoys Q20 and Q22 at 4642'33 north latitude and 07128'18 west longitude. At 0445 the speed was increased to half ahead and then full ahead. The vessel remained immobile, course 256.5G. On board the LT ARGOSY it was observed that the vessel was south of the Pointe--Basile range when the wheelhouse was abeam of the bow of the G.ORDZHONIKIDZE. At 0448, the main engine of the G. ORDZHONIKIDZE was stopped. The decision was made to try to refloat the vessel, and at 0449 the speed slow ahead was ordered, but the attempt was unsuccessful. At 0453 MCTS Quebec City was informed that the vessel was resting on the north edge of the channel with a list to port. At 0459 the main engine was stopped again, waiting for the rising tide. Because of the strong current setting to the east, the crew could not take soundings around the vessel, but sounding of the vessel's compartments indicated no ingress of water. At 0640, in the presence of a flood current, the vessel was refloated under its own power and proceeded toward the port of Trois-Rivires, Quebec. Abreast of the Saint-Augustin shoal, the channel is dredged to a depth of 10.7 m over a distance of approximately 1.5 nautical miles between buoys Q19 and Q22. There is an anchorage area upstream and downstream of this dredged channel. An operational directive instructs vessel traffic regulators to inform vessels in transit of any special situation that might be the cause of a potential conflict between ships. Draught is one of the major parameters affecting vessel manoeuvrability on the St. Lawrence River; vessels whose draught is greater than 9.14 m (30 ft) are considered to have a deep draught, and represent a special situation. Accordingly, mariners are informed of this special situation over the MCTS radio telephone when they report to the calling-in points. The marine usage established by pilots is to avoid overtaking in a restricted channel (except in special circumstances) when the two vessels are subject to this special situation. In an overtaking situation in a restricted channel, the vessels are subject to the hydrodynamic forces created by the interaction between the ships, the suction effect and the bank effect. The short distance between the vessels produces a change of hydraulic pressure around the two hulls. This hydrodynamic interaction is composed of lateral and longitudinal forces and turning moments. The combination of these hydrodynamic forces reduces directional control of the vessel.